1. Field of the Invention
The present invention relates to work holders, and more particularly to a swing clamp for holding a workpiece.
2. Description of the Prior Art
Powered work clamping devices, or swing clamps, are typically used on machine tools to hold a workpiece on a table or jig while a mechanical operation such as milling, drilling or grinding is performed. Swing clamps may be manually, hydraulically or pneumatically powered.
Swing clamps typically are controlled by solenoid actuated, two-position flow control valves for controlling the flow of fluid to and from the clamp. A single control valve was disclosed and claimed in U.S. Pat. No. 4,560,152 assigned to the same assignee as the present invention. In general, prior clamps relied on motion of a rotatable piston in opposed axial directions concurrently with rotation of a work-engaging head secured to the piston. The present invention operates from independently operated, solenoid actuated, two-position valves which alternatively act upon swing clamp components to provide independent axial motion of the plunger relative to rotational motion of the work-engaging head.
The principal advantage provided by the clamp of U.S. Pat. No. 4,560,152 was that the working head plunger extended and rotated 90 degrees with only ne "on" signal and with only one control port, thus simplifying plumbing and providing flat rotation of the working head.
Several additional patents known to the present inventor will now be described, it being apparent from the descriptions that the independent relative axial and rotational motion of the work-engaging heads described therein has not been taught nor suggested by any of the prior art devices.
A device comprising a pivoted lever and power means for actuating the same is disclosed in the Northern et al U.S. Pat. No. 3,173,673 granted Mar. 16, 1965 in which a pivoted lever and power means for actuating the same are characterized by rotatable mounting means for the lever providing swing work-clearing movement, in addition to the pivotal, work-clamping and releasing movement thereof and which further requires additional power means connected to the lever and operably coupled to the first power means for sequential operation of the lever movements for swinging into position before pivotal closing and preferably also for pivotal opening before swinging out. This device further includes two separate operating pistons and a housing formed by complex machining operations and additional means dependent on proper rotational positioning of the clamping lever before a secondary plunger positively engages the lever for clamping action.
U.S. Pat. No. 3,362,301 granted to Kohlitz on Jan. 9, 1968 discloses a fluid actuated clamp having a main piston for alternative axial movement of the shaft holding the work-engaging head and two transversely operating pistons for rotating the head as it is being raised or lowered upon release of the piston from interengagement with a tongue and groove
An actuating mechanism for a work-engaging clamp was disclosed by Rowe in his July 29, 1969 U.S. Pat. 3,457,838, wherein there is disclosed simultaneous axial and rotational movement of the work-engaging head by means of a cam and cam follower. Similar cam operated members following a cam follower, either disposed directly on the piston shaft or in the wall of the bore slidably retaining the shaft, are shown in the U.S. patents granted to Sessody (assigned to the same assignee as the present invention) and bearing U.S. Pat. No. 3,572,216 with an issuing date of Mar. 23, 1971, a later issuing Sessody U.S. Pat. No. 3,605,569 granted Sept. 20, 1971, U.S. Pat. 3,948,502 granted Apr. 6, 1976 to Waller et al, U.S. Pat. No. 4,265,434 granted May 5, 1981 to Hamilton et al and U.S. Pat. No. 4,351,516 granted to Erosoy et al Sept. 28, 1982.
It is apparent from reviewing these patents that it is important to provide a means for both raising and lowering a work-engaging clamping head independently of means for rotating the head to facilitate insertion and removal of a workpiece relative to a supporting worktable. In addition, the present invention provides a means of minimizing the number of control ports, thereby minimizing hoses and valving which complicate plumbing, fixturing and are "chip traps" in machining operations, which often restrict the use of swing clamps.
Typical swing clamps only achieve two controlled positions (extend and retract) with two independent signals applied to respective control ports. Each of the prior art patents teach simultaneous and dependent operation of the work-engaging head with relation to its raising and lowering actuator means. The patents do not provide the versatility of independent operation which may be controlled by either sequential or selectively independent introduction of pressurized fluid to permit a variety of clamping positions as desired.